Brumbies coach Dan McKellar says it would be a risk to start incumbent Wallabies loosehead prop Scott Sio in their Super Rugby season opener.

The 27-year-old has been overlooked for Friday night's clash with Melbourne at GIO Stadium in favour of former Queensland captain James Slipper.

Sio was Australian coach Michael Cheika's choice as starting loosehead prop in their November Test against England. But Slipper will have first crack in the No.1 jersey after being thrown an offseason lifeline by the Brumbies. This followed a tumultuous final season at the Reds, where he battled injury, depression and twice tested positive for cocaine.

Sio was among three Wallabies to be rested for the Brumbies' trial wins against the Rebels and NSW Waratahs. While David Pocock and Allan Alaalatoa have been picked in the starting XV, the 53-Test prop will come off the bench.

"I'd spoken to Scotty about it two weeks ago that that was my thinking and he understands," McKellar said. "To go into the first game of the year, without any trial footy under his belt and start the game, would be a bit of risk."

Slipper impressed in the Brumbies' first trial, but suffered a rib injury last week against the Tahs and took himself to the bench after 25 minutes.

The Brumbies will face a Rebels side down two first-choice Wallabies but one that includes club debutant Quade Cooper. The former Wallabies playmaker took part in one trial match but will start his first Super Rugby game for the Rebels alongside good mate Will Genia.

Isi Naisarani will join Cooper in making his Rebels debut after the Fijian switched clubs from the Brumbies during the offseason.

The news was not as good for Wallabies duo Reece Hodge and Adam Coleman however, after they were ruled out of the season opener through injury.